Programmable array logic circuit employing non-volatile ferromagnetic memory cells

ABSTRACT

A programmable array logic circuit whose temporary memory circuitry employs single bit non-volatile ferromagnetic memory cells. The ferromagnetic memory cells or bits store data even when there is no power provided to the circuitry, thus saving power during operation of the programmable logic circuitry, and ensuring that there is no loss of the data should there be a temporary power shut down. Additionally, the ferromagnetic cells provide for indefinite number of switching actions on the data without degradation to the capacity to store data therein. The invention provides an integrated circuit, comprising a programmable logic circuit array having product lines and input lines therein, and a storage register circuit. The storage register circuit has a ferromagnetic bit and sensor coupled to store a remnant control signal and an output transistor, coupled to be responsive to the remnant control signal on its gate, and coupled between an input and product line. Additionally, the integrated circuit may further include a logical AND array and a logical OR array.

This application is a continuation of co-pending U.S. application Ser.No. 11/889,908, which was filed Aug. 17, 2007, and is allowed, which isa continuation of U.S. application Ser. No. 11/580,064, which was filedOct. 13, 2006 and issued as U.S. Pat. No. 7,285,983, which is acontinuation of U.S. application Ser. No. 11/037,696, which was filed onJan. 18, 2005 and issued as U.S. Pat. No. 7,123,050, which is adivisional of U.S. application Ser. No. 10/239,133, which was filed Jan.20, 2001 and issued as U.S. Pat. No. 6,864,711, which was a U.S.national phase of International Application Number PCT/US01/01793, whichwas filed Jan. 20, 2001, which claims the benefit of No. 60/177,533filed Jan. 21, 2000.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates generally to a programmable array logiccircuit employing non-volatile ferromagnetic memory cells. Moreparticularly, the present invention uses a non-volatile ferromagneticmemory cell to temporarily store binary data.

2. The Background Art

Programmable logic devices have any number product sets, usually ingroups of four (4), eight (8), sixteen (16) or more bits, although often in groups often (10). The arrays are programmed forapplication-specific tasks to be performed within digital electroniccircuits. The fusible link types cannot be re-programmed, but thoseemploying EEPROM and Flash can. For those PALs which use fusible links,the data in the “D” registers is lost at power off. For those that useEEPROM and Flash as replacements for the “D” registers, data is not lostat power off time.

Up to the present, traditional PALs have used “D” type flip-flops forproduct registers. Lately, however, some fabricators have begun usingEEPROM and Flash technology to replace these. These last twotechnologies have draw-backs, however. EEPROMs are cumbersome tore-program, both are slow to re-program, exhibit “write fatigue,”thereby limiting their useful life, and must be mass-written tore-program.

SUMMARY OF THE INVENTION

It has been recognized that it would be advantageous to develop aprogrammable array logic circuit whose temporary memory circuitryemploys single bit non-volatile ferromagnetic memory cells.

It is an advantage of the invention to have the ferromagnetic memorycells or bits to store data even when there is no power provided to thecircuitry. Thus, saving power during operation of the programmable logiccircuitry, and ensuring that there is no loss of the data should therebe a temporary power shut down.

Additionally, the ferromagnetic cells provide for indefinite number ofswitching actions on the data without degradation to the capacity tostore data therein.

The invention provides an integrated circuit, comprising a programmablelogic circuit array having product lines and input lines therein, and astorage register circuit. The storage register circuit has aferromagnetic bit and sensor coupled to store a remnant control signal,and an output transistor, coupled to be responsive to the remnantcontrol signal on its gate, and coupled between an input and productline.

Additionally, the integrated circuit may further include a logical ANDarray and a logical OR array.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, taken in conjunction with theaccompanying drawing, which together illustrate by way of example, thefeatures of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a preferred embodiment of the presentinvention.

FIG. 2 is a schematic of a preferred embodiment of the presentinvention.

FIG. 3 is a cross sectional view of a single ferromagnetic memory bit.

FIG. 4 is a schematic of a field programmable logic device capable ofutilizing the present invention.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the exemplary embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended. Any alterations andfurther modifications of the inventive features illustrated herein, andany additional applications of the principles of the invention asillustrated herein, which would occur to one skilled in the relevant artand having possession of this disclosure, are to be considered withinthe scope of the invention.

For the purpose of providing background material which may in somerespects illustrate the state of the art, the following books are hereinincorporated by reference for non-essential material: “ProgrammableLogic Handbook,” fourth edition, by Monolithic Memories Inc., 2175Mission College Blvd., Santa Clara, Calif.; and “Practical Design UsingProgrammable Logic,” by D. Pellerin and M. Holley, Prentice Hall,library of Congress no. TK7872.L64 1991.

The following United States patents are herein incorporated by referencefor their supporting teachings:

U.S. Pat. No. 5,300,830, is a programmable logic device macrocell withan exclusive feedback and exclusive external input lines for registeredand combinatorial modes using a dedicated product term for control.

U.S. Pat. No. 5,287,017, is a programmable logic device macrocell withtwo OR array inputs.

U.S. Pat. No. 5,324,998, is a zero power re-programmable flash cell fora programmable logic device.

U.S. Pat. No. 5,295,097, is a nonvolatile random access memory.

U.S. Pat. No. 5,867,049, is a zero setup time flip flop.

U.S. Pat. No. 5,298,803, is a programmable logic device having low powermicrocells with selectable registered and combinatorial output signals.

The invention is used in the normal arena in which PALs are employed,but where it may be advantageous to retain the last data stored afterremoval of power to the circuit as well as the simplicity of randomre-programming. This PAL circuit could be in all manner of digitalcircuitry, including computers, robotics, telephonics, automotivecircuits, security devices, and so on. The advantages over prior art lieprincipally in that PAL devices using ferromagnetic digital memory cellsfor product registers would enjoy non-volatility, high-speed in siturandom re-programmability and indefinite long life span.

A PAL having product registers (flip flops) that use non-volatileferromagnetic memory/storage cells for product storage registers isdescribed wherein the non-volatile ferromagnetic memory cells, comprisedof single stick-like ferromagnets whose aspect ratio is greater than 1:1(height to width), are fabricated normal to the plane of the substratewith a sensor centered intimate to, and at one end of the ferromagnetsare used for these functions. The magnetic polarity of eachferromagnetic memory cell bit is coerced into reversal using write, orstate change circuitry, comprised of a coil which surrounds, up to andincluding 270°, and is intimate to, the ferromagnetic stick. The writecurrent in each coil is bi-directional, depending on the desiredmagnetic movement, or polarity, of the bit. The output of the sensorreflects the binary condition of the bit, and is used as binary dataoutput for product registers.

FIG. 1 is a schematic of a dual output storage register 9, or flip-flop,which is comprised of a ferromagnetic memory cell consisting of micronor sub-micron-sized ferromagnetic bit whose aspect ratio is greater than1:1 (i.e., 2:1, etc.), deposited normal to the plane of the substratewith its attendant support circuitry. Uniquely, there is a ferromagneticstick (bit) 1, which is at least partially, but not necessarilycompletely, surrounded by a write drive coil 2. The bi-directionalcurrent in the write drive coil sets the polarity of the bit and isswitched by two sets of transistor pairs, or switches. The firsttransistor pair being Q3 and Q6, having reference number 4 a, and thesecond pair being Q4 and Q5 having reference number 4 b. These switchesare in turn gated by Q1 and Q2, having reference number 8, both of whichare “on” when either of the SET 25 or RESET 26 lines are inactive, orpositive in polarity. Q7 and Q8, reference number 7, are the SET andRESET switches. When one or the other of the SET or RESET lines isappropriately pulsed, the associated gate is opened to allow ground tobe coupled to line 20 or 21 and thus pulling them low.

On a second portion of the flip-flop 9, or storage register circuit,there is a ferromagnetic bit field sensor 3, which is capable of sensingremnant polarity stored in the bit 1. It is noted that the dashed lineis meant to illustrate the fact the sensor 3 is to be physically locatedproximate the top or bottom of the ferromagnetic bit 1, but isillustrated at a spaced relationship for schematic purposes only and notmeant to illustrate physical layout as is shown in FIG. 3. Wherein,amplifier U1, having reference number 5, responds to the signal based onthe Hall voltage that appears across the sensor 3. The outputs are fedto an output transistor Q9, having reference number 6, which in turnallows input line 22 to be coupled to product line 23 when the output ofthe storage register 9 opens the gate on the output transistor Q9.

Since the ferromagnetic bit does not change state when power to thecircuit is off, when power has thereafter been restored subsequent to apower off, the storage registers will have retained their critical data.Additionally, even while there is power to the programmable logicdevice, it is noted that additional power is not required to maintainthe stored state in the flip-flop 9, thus, saving overall powerconsumption.

FIG. 2 is a representation of the “SR” type register or flip-flop 9 ofFIG. 1 and is connected to the product circuitry of a typical PALproduct array 24. It is noted that one skilled in the art will easilyrealize that the bit 1 will store a remnant polarity in the materialthat the sensor 3 will sense. Thus, creating a remnant control signalthat will cause the amplifier 5 to constantly open or close the gate ofoutput transistor 6. Where the polarity of the bit will exist even afterthe power to the circuitry has been turned off. Thus, to read theproduct line signal, it is only needed to provide power to the amplifier5. Where to change the remnant polarity, the SET and RESET controlcircuitry is needed to be activated.

FIG. 3 depicts, for example, a potential cross-section of a micron orsub-micron scale ferromagnetic memory cell with the sensor shown on thebottom; however, the sensor can be on the top as well. There is nofunctional difference between these configurations. They demonstratethat either construction can be employed. There is a ferromagneticstorage element 11, or “bit,” a sensor 12, a sample drive line 14, whichis made of Al, Cu or any other suitable conductor material. Additionallythere is a cutaway of the set (write) drive coil 13 that wraps aroundbit 1. In this depiction, matrix interconnects are not shown for thesake of clarity. The entire memory cell rests on substrate 19, which canbe silicon, glass, GaAs, or other suitable material. Insulation layer 15resides between the ferromagnetic bit 11 and the set coil 13. Insulationlayer 15 can be of a material such as SiO 2 or Si3N4, etc. There is anoverall insulation sections 16, 17 and 18, again made of SiO2, Si3N4, orother suitable material.

It is noted that there are currently several designs that are currentlybeing developed by the current inventive entity regarding the layout ofthe ferromagnetic bit and its accompanying sensing circuitry that willbe functionally equivalent to the circuitry disclosed in FIG. 3.

Several methods may be employed to make this cell, including, but notlimited to, electroplating, sputtering, E-beam deposition, chemicalvapor deposition and molecular beam epitaxy.

Referring to FIG. 4, there is an embodiment of the invention beingutilized in a field programmable logic device. One skilled in the artwill recognize that there is a programmable AND array with inputs andoutputs. Similarly, there are two programmable OR arrays that routesignals through various levels or numbers of logical OR gates before thesum of products are sent to designated macrocells. It is noted that theintersections of the AND and OR arrays (the lines) will have one of theflip-flops 9 located thereat to allow for product calculation asillustrated in FIG. 2.

It is understood that the above-described arrangements are onlyillustrative of the application of the principles of the presentinvention. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the spiritand scope of the present invention and the appended claims are intendedto cover such modifications and arrangements. Thus, while the presentinvention has been shown in the drawings and fully described above withparticularity and detail in connection with what is presently deemed tobe the most practical and preferred embodiment(s) of the invention, itwill be apparent to those of ordinary skill in the art that numerousmodifications, including, but not limited to, variations in size,materials, shape, form, function and manner of operation, assembly anduse may be made, without departing from the principles and concepts ofthe invention as set forth in the claims.

1-2. (canceled)
 3. An integrated circuit, comprising: a) A programmablelogic circuit array having product lines and input lines therein; and b)a storage register circuit, having i) a ferromagnetic bit and sensorcoupled to store a remnant control signal; ii) a write drive coil; andiii) an output switch.
 4. The integrated circuit of claim 1, wherein theferromagnetic bit is at least partially surrounded by the write drivecoil to set the polarity of the ferromagnetic bit.
 5. The integratedcircuit of claim 1 wherein the output switch is coupled to be responsiveto the remnant control signal, and coupled between an input line and aproduct line.
 6. The integrated circuit of claim 1, wherein the storageregister circuit further includes a sensor positioned proximate to theferromagnetic bit, to sense the polarity of the ferromagnetic hit and tocreate the remnant control signal therefrom.
 7. The integrated circuitof claim 4, wherein the output switch is a transistor having a gatecontrolled by the remnant control signal.
 8. The integrated circuit ofclaim 4, wherein the programmable logic array further comprises alogical AND array.
 9. The integrated circuit of claim 4, wherein theprogrammable logic array further comprises a logical OR array.
 10. Theintegrated circuit of claim 4, wherein the ferromagnetic bit has aheight that is greater than its width.
 11. The integrated circuit ofclaim 8, wherein the storage register circuit has a supporting substrateto support the ferromagnetic bit to have the height orientedperpendicular thereto.
 12. The integrated circuit of claim 9, whereinthe sensor is located below the ferromagnetic bit and above thesubstrate.
 13. The integrated circuit of claim 1, wherein the storageregister circuit has a set and reset input to program the remnantcontrol signal that is to be stored in the ferromagnetic bit.
 14. Theintegrated circuit of claim 1, wherein the write drive coil isbi-directional.